I bought this boat last year. I was never able to get a really healthy idle until 900 RPM. I know it should be happy purring along at 600 RPM, the timing is spot on and all signs pointed to the carb. Visually, it was full of carbon deposits on the choke plate and just looked neglected.

I am hoping that these photos may help someone in the future, if only to provide a visual reference to what goes where. This is my first time rebuilding a four barrel, and I've only rebuilt motorcycle carbs before this. I am learning as I go here.

This is my carb, Holley 4160 list 50419.

As I understand it, the number under the list details when the carb was built. The 297th day of 1986 in this case. I'm not entirely sure if that's true or an old wives tale.

Holley's site provides a great reference for figuring out which kit you need. For my carb they spec'd the 703-29 rebuild kit. Amazon had the best price for me, $36 with free 2-day Prime shipping.

Anyone with a pre-1992 4160 should also consider ordering Holley part 125-500: Power Valve Check Ball Kit. This kit updates the old 4160s to include backfire protection - no more losing your power valve if your engine suffers a backfire. $14 on Amazon. Thank you thatsmrmastercraft!

Suggestion, take a ton of pictures of the small assemblies as you take them apart. This is the choke assembly.

One thing to clean is the choke breather screen. This provides some fresh air to the electric choke and keeps it from overheating. The screen on mine was completely full of carbon and I could not even blow through it. Take it out, soak it in carb cleaner and get it transparent again. A blocked breather will kill your choke.

The bowls were pretty clean.

After removing some of the easy things, I gave the body a long dunk in my $70 Harbor Freight ultrasonic cleaner. I turned it every few minutes and after the initial hour or so I'll drain the dirty solution and rinse the parts with water.

Later, before assembly I'll run them through and rinse them again.

I have found this cleaner to be much more effective than the carb cleaner soaks I used to give my dirty carb parts.

This thing works wonders, and I use it all the time with motorcycle parts. My solution is 1 part Simple Green and 3 parts water. Turn it on and watch the carbon deposits break up and float away.

That solution was pretty much clear when I started.

The cleaner has a heater, and helps soften up the old gasket material.

At this point, I was pretty certain of at least one problem that was causing my rough low idle. A major vacuum leak -- the primate throttle plates were not snapping fully closed. They would close with some assistance, but they were binding due to "gunk".

The plates would seal up nicely with a little assistance, but they should completely close off without additional assistance (I mean, the return spring should be enough to do the job).

By using a zip-tie, you can get the plate assemblies to stay open while they soak. Deposits have probably built up where they make contact with the throats.

Soaking the body and cleaning the throats did not fully solve the problem, so I knew I would have to remove the primate throttle plates and remove the bore to clean out any deposits that could be causing the friction which was preventing a full close.

These brass screws had to come out in order to remove the plates (so I could slide the shaft out and clean the bores).

Of course, one of the 4 brass screws snapped off. What I wish I knew then, was that the brass screws are "staked" in place which means the ends are mushroomed out to prevent them from ever working themselves lose and finding their way into your cylinders. Of course, this makes them difficult to remove if you did not know this in the first place!

Holley provides a great instruction document here for removing and replacing your throttle blades, should anyone encounter this in the future: http://www.holley.com/data/Products/...99R9978rev.pdf. I wish I would've found that before I snapped the screw, as it calls for filing off the far end of the screw before attempting to unscrew it. Oh well!

With some careful drilling and the help of an 8-32 tap, I got the old screw out of there and cleaned up the threads. I found a pack of new brass screws on eBay and now I just have to wait for them to arrive.

In the meantime, I took the shaft to my polisher and shined up the bearing surfaces on the shaft. I also took a bore brush from my gun cleaning kit and ran it through the throttle body to get any remaining deposits out of there. The assembly snaps shut now.

The rebuild continues. The finish on the bowls looked terrible so I came up with a quick way to return them to bare aluminum. I know it will oxidize eventually, but at least they look "clean" again.

Secondary bowl before.

Once all of the bits were removed, I put them in a bath of 5 parts water to 1 part CLR. Let them soak for 15 - 20 minutes and then took some steel wool to them. A wire brush on a dremel helped knock down the really ugly spots.

Secondary bowl after.

Primary bowl after.

Meanwhile, I soaked the main jets in carb cleaner and then ran them through my ultrasonic.

The new power valve also went in. My original PV was 2.5. The PV Holley sent in the marine rebuild kit was 5.0. I'm going to give it a shot and see how it runs. The 2.5 is still useable so I can always throw it back in if the 5.0 doesn't feel right.

The old gasket was nearly impossible to remove from most of the parts. I used aerosol gasket remover to loosen it. It still took some time with a wire wheel on a dremel to get the parts back to bare metal.

Primary bowl before.

Primary bowl with the new needle & seat, and float set to parallel.

Getting closer to the finish line now... fewer parts left on the table.

As mentioned earlier, Holley part 125-500 is an update for pre-1992 carbs without Power Valve protection. This $14 retrofit will protect your PV in the event of a backfire.

It basically consists of a drill bit set to drill .300" deep, a spring, a ball bearing and a brass retainer.

The power valve orifice on the throttle body is drilled out to .300" deep, the spring inserted followed by the ball and the retainer. I will take a picture of the finished product tonight.

Here are the pictures from the Holley 125-500 installation. It's very simple, and will take all of 10 minutes.

First the passage is enlarged using the provided bit.

Then the three components drop in the hole in this order: Spring (taper facing up), check ball and retaining ring (gently hammered in place).

Final result.

Meanwhile, the brass throttle plate screws I ordered from eBay came in and I was able to remount the primary throttle plates following the instructions from Holley (located here).

As I was assembling the secondary, I thought I'd take a picture to remind that you will need a 5/32" clutch head driver to remove / replace your metering plate. Lots of people have just used a flathead screwdriver, but Ace hardware stocks these drivers for about $7 if you want to use the right tool for the job.

It's all going back together now. After taking this picture, I realized that the choke assembly should go on last (after the secondary diaphragm). Oops. I hope to get this all back on the boat tonight.

Once you get the carb back together, there are a few checks you need to make. One check is that the accelerator pump is not fully extended at WOT. Holley calls for a .015" clearance between the accelerator pump arm and the throttle actuator nut at WOT.

The intake manifold gasket had to be original.

Careful scraping with a shop vac next to me preventing bits from falling in. The carb spacer looked the same but was easier to deal with on my workbench. I cleaned that up and painted it while I had it off.